Ca²⁺ entry through Ca²⁺ release-activated Ca²⁺ (CRAC) channels is an essential step for T-cell activation and proliferation. Although the functional importance of CRAC channels is well documented, its molecular identity is still unknown. Members of the transient receptor potential (TRP) protein family appear to be best candidates to form these channels. We analyzed the expression pattern of TRPs in primary human T-cells (peripheral blood lymphocytes and CD3⁺ cells) and in Jurkat T-cells employing RT-PCR and qRT-PCR. Whereas for example TRPC1 and TRPC3 were detected in both primary and Jurkat T-cells, the expression of other TRPs like TRPC6 was restricted to Jurkats. Therfore these cells seem to be inappropiate for our studies. To investigate the role of TRPs expressed in primary T-cells, we used siRNA technology to down regulate TRP mRNA. The efficiency of siRNA transfection was confirmed by qRT-PCR. Subsequently, we analyzed proliferation and Ca²⁺ signals in siRNA transfected cells. So far, down regulation of TRPC3 resulted in a slight reduction of proliferation rates in T-cells. We conclude therefore that TRPC3 protein is involved in Ca²⁺ signalling of primary human T-cells.

(the first two authors contributed equally)